The invention relates to a hydraulic adjusting device for adjusting the initiation of injection by a fuel injection internal combustion engine of the type having a reciprocating pump shaft driven by a pump shaft roller tappet engaging a rotating crankshaft or the like. Preferred arrangements of the invention relate to such an adjusting device for self igniting internal combustion engines.
In German unexamined published application (DE-OS) No. 29 32 672 a hydraulic adjusting device for high pressure injection systems is disclosed which comprises means for changing the timing of the beginning of injection of fuel into the combustion chamber of the internal combustion engine. With this known arrangement the adjusting characteristics are reached by twisting or rotating the injection pump lifter shaft with respect to the motor crankshaft.
German published examined application DAS No. 1,107,025 relates to an injection pump adjusting arrangement of the kind the present invention is also directed at improving.
The invention is based upon the problem to establish a hydraulic adjusting device which is simple and requires a small construction space, which should not use any coupling connection between the motor crankshaft and the pump lifting shaft, and which rather operates directly on the pump shaft of the injection pump and is of the kind with adjustment characteristics influenced in a desirable manner by varying engine operational data.
This problem is inventively solved by a hydraulic adjusting device of the above mentioned type, in that specific means are provided through which the effective working stroke of the pump shaft is changed.
By adjustment of the effective working stroke of the pump shaft, a precise adjustment of the initiation of injection is obtained which is in contrast to the known adjusting devices arranged outside of the injection pump with resultant longer transfer paths and system irregularities.
A preferred embodiment of the invention provides that the adjusting device is formed at a work chamber bounded by a roller tappet support and with a guided inner piston of the pump shaft, which device shortens the working stroke of the pumping shaft and simultaneously moves the beginning of injection toward an earlier point in time in response to increasing control pressure in the work chamber.
In order to have adjustment of the injection initiation timing with low control pressure in the work chamber on the one hand, in spite of high pretension strength of the spiral or helically formed tappet biasing spring--and on the other hand to achieve a small adjustment movement of the inner piston with respect to the roller tappet support, it is further proposed that a cup spring (Bellville washer) is arranged in the work chamber to act against the tappet spring in such a manner that the cup spring lays substantially completely flat against both the roller tappet support and the inner piston during no or small control pressure effects in the work chamber.
With the arrangement of the cup spring the oil pressure respectively, the control pressure, can be reduced to zero. The spring strength of the tappet biasing spring therefor corresponds at least to the cup spring strength.
The slighest control pressure increase results in movement of the cup spring.
It is further provided according to especially preferred embodiments of the invention that the work chamber for the control pressure oil is connected by means of a control bore leading to a pressure line connected to collective pumping elements of the injection pump during the lower dead center position of the respective associated roller tappet. The pressure connection line extends in the longitudinal outer wall of the housing of the injection pump.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, a single embodiment in accordance with the present invention.